This proposal is aimed at allowing Dr. Joseph K. Wong, a physician completing his Infectious Diseases Fellowship to undertake additional research training and to pursue and expand on a project begun during his fellowship here at UCSD. An individualized and comprehensive program will be built around this research project, incorporating didactic studies and close peer and faculty interactions, to allow Dr. Wong to achieve his goal of developing and maturing into a productive academic investigator in biomedical research. Human Immunodeficiency Virus (HIV) targets and infects CD4 receptor bearing cells including CD4 lymphocytes and cells of monocyte/macrophage lineage. The result of continuous and high levels of viral replication is a progressive depletion of CD4 lymphocytes resulting in a state of immunodeficiency termed AIDS. Lymphoid tissues and the CNS are the two organs most severely affected by direct HIV infection. Information about the turnover and trafficking of virus within and between these organ systems and the peripheral blood is incomplete. Pharmacologic interventions aimed at reducing HIV replication are hampered, in part , by the emergence of drug resistance. Treatment with the reverse transcriptase inhibitor AZT, the most widely used anti-retroviral, results in the appearance of resistant variants in the peripheral blood with well defined genotypes. The extent and timing of emergence of resistant mutants in lymphoid tissues and brain, relative to the peripheral blood require further characterization. A primary aim of this research plan is to examine the viral genotypes with respect to AZT resistance derived from paired autopsy specimens of brain and lymphoid tissue. The region of the pol gene encoding the viral reverse transcriptase (RT) will be sequenced from DNA and RNA extracted from autopsy tissues of patients dying with AIDS. Comparing the relative frequencies of drug resistance-associated genotypes between lymphoid tissue and brain relative to antemortem clinical and treatment histories will help to characterize the organ-specific rates of emergence and disappearance of resistant variants. Comparison of patients having a variety of treatment histories will help to define how long discordant populations can be maintained. A second aim is to study and compare viral genotypes, with respect to AZT resistance, derived from peripheral blood CD4 T-lymphocytes, peripheral blood monocytes, alveolar macrophages, lymph node mononuclear cells and plasma from HIV infected individuals. HIV infected patients will undergo bronchoalveolar lavage(BAL), fine needle percutaneous lymph node aspirate and phlebotomy. Viral RT sequences will be obtained from DNA and RNA extracted from fractionated and purified cell subsets and plasma. Comparison of AZT resistance genotypes derived from these cell types will address whether organ specific differences in viral populations (as seen between lymphoid tissue and brain) can be explained by the nature of the resident target cells or are the result of separate anatomic barriers. The results of these studies may have both therapeutic and pathogenetic implications.